Studying light is central to photography.

So it is not strange that we should look at all its relationships it has within our control.What happens to light after contact with a surface is important. Here we are going to look at some of the effects of contact with different surfaces.

Knowing how light behaves when hitting a surface is important. First, it helps us predict how we might treat it in a photograph because we know what to look for under certain conditions. Second, the effect a surface has on light means we can plan shoots according to the light conditions we encounter, or want to set up in a studio. Reflected light also helps determine the colour, shape and form of an object.

On impact with a surface…

Light is changed by contact with any material. It is reflected, refracted or absorbed. In this article we concentrate on reflection and absorption. Refraction is an important topic for photographers but is a wide study. I will treat it separately another time.

Reflection comes in two main forms. Specular reflection, where light is reflected off the surface and is bounced away. In our Photographic Glossary we have a new article dedicated to Specular Reflection and its behaviour.

In Diffuse Reflection, light hitting a surface is scattered, or diffused, by that surface. The ray of light does not continue in a bounced line… its reflected imperfectly in all directions. A diffuser surface is un-mirror-like. In our Photographic Glossary we have a new article dedicated to Diffuse Reflection and its behaviour.

Colour

Absorption is extremely important to photographers. The absorption/reflection relationship determines colour. The colour of something is created because some wavelengths of light are absorbed and reflected. The mixture of wavelengths being reflected determines the colour – we see only those wavelengths that reach our eye by reflection. A black surface has low reflection. It’s difficult to see because it has a blackness. White is opposite to black almost all the light wavelengths are reflected creating whiteness. Green, the colour to which our eyes are most receptive is the colour of plants. Plants reflect greens strongly. The other wavelengths of light, which they absorb, are used to produce their energy for life (Photosynthesis ).

Absorption beyond colour

Absorption creates heat. When light strikes an absorbing surface the energy is transferred to the surface. The reflection is also dampened. A new main article in our Photographic Glossary explains Absorption.

The real world of light

Models of light, the perfect reflection, diffusion or absorption help us understand the mechanism behind what is going on. Real life is not so clear. Here are a few ideas of how these three behaviours of light affect us as photographers.

Colour, reflection, diffusion, absorption (and refraction) are never perfect. In some man-made materials we see consistent light behaviour across a surface. A mirror is one example. It will have pretty much the same behaviour right across its surface. Colours are less reliable. They vary, sometimes enough for our eye to see – especially once they fade.

We see light as brightness on a surface. Two things affect brightness. The amount of light hitting a surface and the amount of light reflected to our eyes.

A bright light hitting our surface will create a bright reflection to our eye. A dimmer light makes less reflection. So light intensity is easy to understand, bright days create brightness from affected surfaces.

Reflection, diffusion and absorption have a relationship that together determines the amount of reflected light from a surface. Bright light striking a highly absorbing surface will be dimmer than bright light hitting a highly reflective surface. So it is the characteristics of the surface that determine how much light is reflected from one material compared to another. Every material has its own reflective, diffusion and absorption characteristics.

Our eyes see things by detecting contrasts. Shadows, colour, brightness, edges and their contrasts provide markers the brain interprets as shape. Where light is more intensely reflected, say from a curved surface, produces a point-highlight of reflection. Then we see both the curve and its relationship to other planes (surfaces) of the object. The Photographic Glossary has a new article dedicated to Highlights.

Some types of highlights are particularly important. Highlights on a sharp curve concentrate light. This new article in the Photographic Glossary examines Specular Highlights.

Bright specular reflections often form as small points. The brightness of specular highlights often exceeds the cameras ability to reconcile their brightness with other light levels in the image. This causes them to burn out as bright white burnout. This very strong white appearance in the image is too strong. They are artificially brighter in the image than it would be to the eye in real life. This is a severe distraction to viewers. See Simple ideas about distractions in photographs for more detail.

Light reflection, diffusion and absorption affects light leaving a surface. On the surface itself the effects of incoming light creating shade/shadow and brightness also has an impact. To get you started on an understanding of shadow this is useful: Three little known facts about shadows.

Light is simple in models

As the articles in the Photographic Glossary show the ideas are simple. Understanding the relationships in the real world when you put them all together are slightly more complex. However, photography is nothing if not complex. It keeps us learning for life!